2016-12-12 General Committee Agenda

GENERAL COMMITTEE MEETING AGENDA                                                 12 DECEMBER 2016


To ensure that the proposed design would not be substituting any fish habitat resources that
were unlikely to have been inhabited with oysters prior to their removal in the mid 1900’s, a
further assessment of the Noosa River system was undertaken by Ecological Service
Professionals on 25-26 October 2016 (the ESP report).

The ESP report quantified that approximately 9,585m2/yr of oysters were likely to have been
removed from the river system for sale each year through peak harvest season. This was in
addition to an unquantified amount of oyster reef substructures that were dredged to provide
materials for road construction etc.

The ESP report also identified that 16,850m2 of buried or functionally dead oyster beds that are
unable to naturally recruit, remain within the Noosa River System.

The reason natural recruitment has not occurred since the mid 1900’s is attributed to a reduction
in hard oyster reef structures for the oyster spat to recruit on, compared to what was available
prior to dredging.

Where hard structures do exist, they are at an inappropriate profile to facilitate the establishment
of an oyster reef. The reasons include frequent sedimentation over the flat hard substrate level
with the river bed which prohibits successful spat recruitment. Oyster spat recruitment is also
most efficient on other oyster shells, most likely due to the ideal micro water chemistry their own
organism creates.

Oyster reefs that previously existed in Noosa River were established prior to hydrological
changes in the catchment such as excessive forestry in the upper catchment and alteration of the
river mouth in the lower catchment and changes to the benthic geology through oyster dredging.
The lack of natural recruitment since oyster harvesting ceased in the mid 1900’s, and the new
river processes, indicates it is now too difficult for the oysters to recruit their natural reef
establishment processes on their own and assistance is needed to provide the vertical profiles
and structures best suited for the natural recruitment processes.

Establishment of a vertical profile, as is proposed in the oyster restoration unit’s design, will
provide sufficient surface areas throughout the under structure for the oyster spat to settle and
continue growing even where sediment and algae establish on the top.

Further, the results of recent studies identified that the vertical profile provided by oyster reefs (as
opposed to flat oyster beds) have been shown to establish different microclimates and therefore
may provide additional levels of resilience for aquatic organisms in changing water temperatures
associated with climate change. Therefore, supporting restoration of lost oyster bed
environments in the Noosa River system can be seen as demonstrating Noosa Council’s
commitment to improving climate change adaptation for our environmental resources.

The conceptual diagram below demonstrates why restoration units are necessary to assist the
establishment of the natural oyster spat recruitment process.




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